This invention relates in general to web tension-control apparatus and more particularly to tension-control apparatus for ink ribbons employed in serial printer applications.
In devices in which any web material is to be delivered or transferred from a rotatable reel, drum, spool, spindle or a like receptacle to another similar and compatible receptacle, it is normally necessary to provide means for maintaining a certain amount of tension in the web material during its deliverence. Tension is desired in the web material for economic reasons and user acceptance during the transfer so that a greater amount of web material may be placed on each receiving receptacle and so the web material will be tightly wound on the receiving receptacle and will not fall therefrom during handling. In addition, it is desired to provide means to brake the supply receptacle in the event the web material breaks so the supply receptacle will not continue to feed the web material. In the particular environment of ink ribbons employed in serial printers, a certain amount of tension is required for proper ribbon feed and acceptable print quality of the printed material.
Although the invention is applicable to various web, tape, strand and ribbon-like materials, it has been found particularly useful in the environment of ink ribbons as used in serial printers. Therefore, without limiting the meaning of the word "ribbon," the invention will be described in this environment.
As any web material is delivered between a pair of reels, drums, spools, spindles, etc., the tension therein will tend to vary due to geometrical and inertial changes. In a serial printer ribbon system, a certain amount of variation in the tension in the ribbon does not adversely affect the ribbon feed or the print quality. In order to wind an ink ribbon onto its take-up spool, it is necessary to apply a force to the take-up spool. The amount of force required will vary and be dependent upon the amount of ink ribbon presently on the take-up spool. The force normally applied will be the value which will be required to rotate the take-up spool when the maximum diameter of the ink ribbon is wound on the take-up spool. Thus, without some compensation in the system, when only a small amount of the ink ribbon has been wound on the take-up spool, the force applied to the take-up spool is much greater than required and results in a greater tension existing in the ink ribbon than when the take-up spool is nearly full of ink ribbon. A fabric ribbon is less susceptible to changes in tension than the matrix type plastic ribbon since it does not stretch nor break as easily and it more easily conforms to the physical shape of the character during the printing action.
An excessive amount of tension in the ribbon can cause the ribbon to stretch and wrinkle and/or fold over onto itself about the deformed center portion or to break, all of which obviously affect the print quality. Also, an excessively low ribbon tension can allow the ribbon to move from its print position to a degree which causes partial or total loss of printing of characters.
It is well known in the art to continuously vary the braking of the wind-off reel in dependence of the tension in the wound-off web material and to rapidly stop the wind-off reel in case of disruption of the web material as disclosed in U.S. Pat. No. 3,243,137. It is also known to use a pawl and ratchet brake device as disclosed in U.S. Pat. No. 3,442,366 to control ribbon tension in an incrementing ribbon feed system. In U.S. Pat. No. 3,621,968, a roller and spring arrangement is disclosed to provide tension in an endless ribbon within a ribbon cartridge. In U.S. Pat. No. 3,797,773, apparatus is disclosed for maintaining tension in a ribbon, which is being wound on an intermittently driven take-up spool by the use of a reed switch (having a tapered shunt) to control a motor which drives the take-up spool. U.S. Pat. Nos. 531,402, 1,340,710 and 1,364,259 disclose various type brake-drag means applied to the side of spool to provide brake and/or tension in the material.
Such prior art solutions have utilized mechanical or a combination of mechanical/electrical means to provide the necessary control of the tension in the web material.
With these prior art problems in mind, it is an object of the present invention to maintain the tension in a ribbon-like member substantially uniform during its transfer from a supply spool to a take-up spool.
Another object of this invention is to improve feeding and braking of web material transferred between two spools or reels.
Yet, another object of this invention is to improve the performance of ink ribbons contained in cartridges of the type used in serial printers.
A further object of this invention is to shape a drag-pad friction device operating on the side of a reel or spool of material in a highly efficient configuration.
Still a further object of the current invention is the construction of an economical method and apparatus for braking ink ribbons for serial printers.
Other objects and advantages will be evident from the specification and claims and the accompanying drawing illustrative of the invention.